This invention relates to a method of manufacturing a semiconductor package on a leadframe. The invention is particularly suitable for, but not limited to, semiconductor packages that are mounted on leadframes which are trimmed from a strip after semiconductor dies have been encapsulated.
Leadframes are employed during the manufacture of semiconductor packages. The advantage of lead frames is that leads of a semiconductor package can be kept in a desired position relative to each other and an associated flag (die mount) during wire bonding to a die and encapsulation of the die. Examples of known leadframes are disclosed in U.S. Pat. Nos. 5,882,955 and 5,889,317 both by Huang, Chih-Kung et al, and both assigned to Sitron Precision Co., Ltd.
A conventional leadframe has a flag portion coupled to peripheral portions by tie bar portions, and lead portions that extend inwardly from the peripheral portion towards the flag portion. Dam bar portions extend between adjacent lead portions, as well as between, lead portions and the peripheral portions.
A typical semiconductor packaging process comprises the steps of mounting a semiconductor die on the flag portion, connecting wires between the semiconductor die and free ends of the lead portions, and encapsulating the semiconductor die, the flag portion, the free ends of the lead portions and the wires in mold compound, to form a semiconductor package on the leadframe. Next, during a trim and form operation, the dam bar portions are cut away, and the lead portions are severed from the peripheral portions and bent to a predetermined shape. Finally, the tie bar portions are severed, thus separating the semiconductor package from the leadframe. The semiconductor packages are then individually tested. Handling individual semiconductor packages during testing is difficult, in part due to their small size, and in part due to the need for each of the semiconductor packages to be arranged in a particular orientation for testing. Another problem is defects, such as bent leads, caused by handling.
To reduce these handling problems, an approach that has been considered is to test the semiconductor packages while they are attached to the leadframe by the tie bar portions, i.e. before severing the tie bar portions. However, since all the flag portions on a leadframe are electrically coupled by the tie bar portions to the leadframe, effectively, this structure shorts all the flag portions together. In order to test the semiconductor packages on the leadframe, the semiconductor packages need to be electrically isolated.
Conventionally, removing the dam bar portions, severing and forming the lead portions, and severing the tie bar portions is performed by an integrated process utilizing in-line automated equipment. A disadvantage of testing first, then severing the tie bar portions is the interruption of the inline process. Another disadvantage is that, after testing, a leadframe must now be loaded onto a machine to sever the tie bar portions. These disadvantages reduce the efficiency of the semiconductor packaging process.